Research on avoidant personality disorder and social anxiety disorder suggests that the main difference between the two is

in avoidant personality behavior people feel inferior being around other people while in social anxiety disorder people do not feel inferior.

Explanation:

The difference that those with social anxiety have when compared with those with avoidant personality, is that these persons with social anxiety do not regard themselves to be inferior amongst other people. They are socially awkward people, who see themselves as equals among other people. They have irrational fears.

Those with avoidant personality disorder have the belief that they are inferior to other people so they feel they deserve/ bound to be rejected and humiliated.

answer; opportunity cost;

i think it should be c